Transfer hydrogenation process and catalyst

ABSTRACT

A catalytic transfer hydrogenation process is provided. The catalyst employed in the process is a metal hydrocarbyl complex which is coordinated to defined bidentate ligands substituted with at least one group selected from an optionally substituted sulphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group, or an optionally substituted sulphonated heterocyclyl group. Preferred metals include rhodium, ruthenium and iridium. Preferred bidentate ligands are diamines and aminoalcohols, particularly those comprising chiral centres. The hydrogen donor is advantageously a secondary alcohol or a mixture of triethylamine and formic acid. The process can be employed to transfer hydrogenate ketones and imines, which are preferably prochiral. Catalysts for use in such a process are also provided.

This is a 371 national phase filing based on PCT/GB01/05285, which was filed Nov. 29, 2001 and claims priority benefit of United Kingdom Application No. 00298356.3, filed Dec. 1, 2000.

The present invention relates to transfer hydrogenation and encompasses processes for transfer hydrogenation, e.g. for producing optically active compounds and catalysts for use in such processes.

Numerous catalysts (generally comprising a transition metal) are known for effecting transfer hydrogenation. The following disclosures are of relevance.

-   (1) Noyori et al; J.A.C.S., 1995, 117 7562–7563: which discloses     that use of     chloro-ruthenium-mesitylene-N-monotosyl-1,2-diphenylethlyenediamine     as catalyst in the transfer hydrogenation of acetophenone to     1-phenylethanol by propan-2-ol gave up to a 95% yield of product     having 97% entantiomeric excess. Similar results were obtained     starting from other alkylaryl ketones. -   (2) Noyori et al: J. Chem.Soc.Chem, Commun, 1996, 233–234: which     discloses catalysts similar to those of (1) above but containing     other alkylbenzene ligands and various beta-amino alcohols in place     of diphenylethylenediamine. The preferred arene ligand was     hexamethylbenzene. -   (3) Our earlier WO98/42643 which discloses transfer hydrogenation     catalysts incorporating an optionally substituted cyclopentadienyl     group co-ordinated or otherwise bonded to a metal (e.g. ruthenium,     rhodium or iridium) capable of catalysing transfer hydrogenation.     The hydrogenation of compound containing carbon-carbon,     carbon-nitrogen, carbon-oxygen and carbon-sulphur double bonds is     disclosed. -   (4) Our earlier WO00/18708 discloses transfer hydrogenation of     iminium salts (including protanated imine salts and quaternary imine     salts) using catalysts of the type disclosed in (1) to (3).

The catalysts used in (1)–(4) whilst being effective for transfer hydrogenation have the disadvantage that they are difficult to recover from the product mixture.

This gives rise to a number of problems. Firstly, the catalysts are relatively expensive and the fact that at least a portion of the catalysts may not be recoverable adds to the expense of the hydrogenation process. Secondly, the fact that catalyst is present in the final product may prevent application of the hydrogenation process to the production of pharmaceutical and veterinary products since administration of the catalyst residue to humans or animals is undesirable.

It is therefore an object of the present invention to obviate or mitigate the abovementioned disadvantage.

According to a first aspect of the present invention there is provided a process for the transfer hydrogenation of an organic compound having a carbon-carbon or carbon-heteroatom double bond, said process comprising reacting said organic compound with a hydrogen donor in the presence of a catalyst having the general formula:

in which:

R¹⁸ represents an optionally substituted hydrocarbyl or perhalogenated hydrocarbyl ligand;

A represents —NR¹⁹—, —NR²⁰—, —NHR¹⁹, —NR¹⁹R²⁰ or —NR²⁰R²¹ where R¹⁹ is H, C(O)R²¹, SO₂R²¹, C(O)NR²¹R²⁵, C(S)NR²¹R²⁵, C(═NR²⁵)SR²⁶ or C(═NR²⁵)OR²⁶, R²⁰ and R²¹ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁵ and R²⁶ are each independently hydrogen or a group as defined for R²¹;

B represents —O—, —OH, OR²², —S—, —SH, SR²², —NR²²—, —NR²³—, —NHR²³, —NR²²R²³, —NR²²R²⁴, —PR²²— or —PR²²R²⁴ where R²³ is H, C(O)R²⁴, SO₂R²⁴, C(O)NR²⁴R²⁷, C(S)NR²⁴R²⁷, C(═NR²⁷)SR²⁸ or C(═NR²⁷)OR²⁸, R²² and R²⁴ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁷ and R²⁸ are each independently hydrogen or a group as defined for R²⁴;

E represents a linking group;

M represents a metal capable of catalysing transfer hydrogenation; and

Y represents an anionic group, a basic ligand or a vacant site;

provided that when Y is not a vacant site that at least one of A or B carries a hydrogen atom, characterised in that at least one of said groups R²⁰ to R²² or R²⁴ to R²⁸ is present in the form of an optionally substituted sulphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group, or an optionally substituted sulphonated heterocyclyl group.

According to a second aspect of the present invention there is provided catalysts as defined in the preceding paragraph.

As used herein (and unless the context otherwise requires) the term “sulphonated” is intended to cover the presence of the sulphonic acid moiety (—SO₃H) and salts thereof. Alkali metal (particularly sodium and potassium) sulphonates are preferred examples of sulphonate groups. Furthermore the enhanced solubility of the ligands (as provided by the polar sulphonate group) gives rise to the possibility of conducting hydrogenation reactions in water, other polar solvents, biphasic systems and in support polar phase catalysis. Alternatively, the sulphonate group may be present in the form of an anhydride (e.g. partially derived from a CO₂H group).

The catalytic species is believed to be substantially as represented in the above formula. It may be introduced on a solid support.

The transfer hydrogenation process may for example be conducted as a homogenous reaction of the type disclosed in (1) to (4) above and the hydrogenated product obtained by standard make-up procedures such as extracting the product mixture with water (e.g. after dilution of the mixture with diethyl ether) and then drying the organic layer over, for example, magnesium sulphate followed by filtration and evaporation of solvent.

The presence of the polar sulphonate group does however give rise to the possibility of effecting the reaction and/or product recovery in various ways.

Thus, for example, at the end of the reaction there may be added to the product mixture an ion exchange resin so that the catalyst becomes immobilised on the resin by virtue of its sulphonate group. The product mixture may then be decanted from the resin and the product recovered with minimal or no catalyst residue. Accordingly, a further aspect of the present invention comprises a process of the first aspect of the present invention, further comprising an additional step of adding an ion exchange resin after reacting the organic compound with the hydrogen donor in the presence of the catalyst.

Alternatively the catalyst may be used as a “supported liquid phase catalyst” which comprises a support (e.g. beads) coated with a thin film of the catalyst dissolved in water or other polar solvent. The transfer hydrogenation phase is then effected by providing the support in the bulk organic phase (containing the hydrogen donor and the substrate to be hydrogenated) of the reaction. The base that is normally required for the reaction may be provided in either the film on the beads or dissolved in the bulk organic phase. Hydrogenated product will be produced in the bulk organic phase which, at the end of the reaction, may be decanted from the solid phase for recovery of the product. This procedure has the advantage of ensuring no or minimal catalyst residue in the first product.

As stated above, the catalyst incorporates at least one group R²⁰ to R²² or R²⁴ to R²⁸ which is an optionally substituted sulphonated hydrocarbyl, sulphonated perhalogenated hydrocarbyl or optionally substituted sulphonated heterocyclyl group. The catalyst may incorporate at least one further R²⁰ to R²² or R²⁴ to R²⁸ group in the form of an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or optionally substituted heterocyclyl group where the substituent(s) if present is/are other than sulphonate group(s). For convenience in the following description reference will be made to the types of hydrocarbyl, perhalogenated hydrocarbyl and heterocyclyl groups which may be used for R²⁰ to R²² or R²⁴ to R²⁸ (as well as groups R¹⁻¹⁷), it being understood that the sulphonated form of R²⁰ to R²² or R²⁴ to R²⁸ may be a sulphonated form of the moieties described therefore.

The process of the invention effects hydrogenation of a carbon-carbon or carbon-heteroatom double bond in an organic compound. Examples of the heteroatoms that may form part of the double bond include oxygen, sulphur and nitrogen. Examples of organic compounds that may be hydrogenated by the process of the invention are of formula I:

wherein:

X represents O, S, CR³R⁴, NR⁵, (NR⁶R⁷)⁺Q⁻, N⁺R⁸—O⁻, (NR⁹OR¹⁰)³⁰Q⁻, NNR¹²R¹³, NNR¹²SO₂R¹⁶, NNR¹²COR¹⁷, (NR¹¹NR¹²R¹³)⁺Q⁻, (NR¹¹NR¹²C(═NR¹⁴)R¹⁵)⁺Q⁻, (NR¹¹NR¹²SO₂R¹⁶)⁺Q⁻, (NR¹¹NR¹²COR¹⁷)⁺Q⁻, NP(O)R¹⁵R¹⁶, NS(O)R¹⁵ or NSO₂R¹⁵.

Q³¹ represents a monovalent anion;

R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹ R¹², R¹³ and R¹⁴ each independently represents a hydrogen atom, an optionally substituted hydrocarbyl, a perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, one or more of R¹ and R², R¹ and R³, R¹ and R⁵, R¹ and R⁶, R¹ and R⁸, R¹ and R⁹, R¹ and R¹¹, R¹ and R ¹², R² and R⁴, R² and R⁷, R² and R¹⁰, R³ and R⁴, R⁶ and R⁷, R⁹ and R¹⁰, R¹¹ and R¹², and R¹² and R¹³ optionally being linked in such a way as to form an optionally substituted ring(s); and R¹⁵, R¹⁶ and R¹⁷ each independently represents an optionally substituted hydrocarbyl, a perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group;

Hydrocarbyl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ independently include alkyl, alkenyl and aryl groups, and any combination thereof, such as aralkyl and alkaryl, for example benzyl groups.

Alkyl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ include linear and branched alkyl groups comprising up to 20 carbon atoms, particularly from 1 to 7 carbon atoms and preferably from 1 to 5 carbon atoms. When the alkyl groups are branched, the groups often comprise up to 10 branched chain carbon atoms, preferably up to 4 branched chain atoms. In certain embodiments, the alkyl group may be cyclic, commonly comprising from 3 to 10 carbon atoms in the largest ring and optionally featuring one or more bridging rings. Examples of alkyl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ include methyl, ethyl, propyl, 2-propyl, butyl, 2-butyl, t-butyl and cyclohexyl groups.

Alkenyl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ include C₂₋₂₀, and preferably C₂₋₆ alkenyl groups. One or more carbon-carbon double bonds may be present. The alkenyl group may carry one or more substituents, particularly phenyl substituents. Examples of alkenyl groups include vinyl, styryl and indenyl groups. When either of R¹ or R² represents an alkenyl group, a carbon-carbon double bond is preferably located at the position β to the C═X moiety. When either of R¹ or R² represents an alkenyl group, the compound of formula (1) is preferably an α,β-unsaturated iminium compound.

Aryl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ may contain 1 ring or 2 or more fused rings which may include cycloalkyl, aryl or heterocyclic rings. Examples of aryl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ include phenyl, tolyl, fluorophenyl, chlorophenyl, bromophenyl, trifluoromethylphenyl, anisyl, naphthyl and ferrocenyl groups.

Perhalogenated hydrocarbyl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ independently include perhalogenated alkyl and aryl groups, and any combination thereof, such as aralkyl and alkaryl groups. Examples of perhalogenated alkyl groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ include —CF₃ and —C₂F₅.

Heterocyclic groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ independently include aromatic, saturated and partially unsaturated ring systems and may constitute 1 ring or 2 or more fused rings which may include cycloalkyl, aryl or heterocyclic rings. The heterocyclic group will contain at least one heterocyclic ring, the largest of which will commonly comprise from 3 to 7 ring atoms in which at least one atom is carbon and at least one atom is any of N, O, S or P. When either of R¹ or R² represents or comprises a heterocyclic group, the atom in R¹ or R² bonded to the C═X group is preferably a carbon atom. Examples of heterocyclic groups which may be represented by R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ include pyridyl, pyrimidyl, pyrrolyl, thiophenyl, furanyl, indolyl, quinolyl, isoquinolyl, imidazoyl and triazoyl groups.

When any of R¹⁻¹⁷, R²⁰⁻²² and R²⁴⁻²⁸ is a substituted hydrocarbyl or heterocyclic group, the substituent(s) should be such so as not to adversely affect the rate or stereoselectivety of the reaction. Optional substituents include halogen, cyano, nitro, hydroxy, amino, thiol, acyl, hydrocarbyl, perhalogenated hydrocarbyl, heterocyclyl, hydrocarbyloxy, mono or di-hydrocarbylamino, hydrocarbylthio, esters, carbonates, amides, sulphonyl and sulphonamido groups wherein the hydrocarbyl groups are as defined for R¹ above. One or more substituents may be present.

When any of R¹ and R², R¹ and R³, R¹ and R⁵, R¹ and R⁶, R¹ and R⁸, R¹ and R⁹, R¹ and R¹¹, R¹ and R¹², R² and R⁴, R² and R⁷, R² and R¹⁰, R³ and R⁴, R⁶ and R⁷, R⁹ and R¹⁰, R¹¹ and R¹², and R¹² and R¹³ are linked in such a way that when taken together with either the carbon atom and/or atom X of the compound of formula (1) that a ring is formed, it is preferred that these be 5, 6 or 7 membered rings. The rings formed in this way may additionally be fused to each other or to other ring systems. Examples of rings which may be so formed include:

wherein X is as defined above and the rings may be optionally substituted or may be fused to other rings.

In certain preferred embodiments, R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R ¹², R¹³, R¹⁴ R¹⁵, R¹⁶ and R¹⁷ are all independently C₁₋₆ alkyl or are a combination of aryl, particularly phenyl, C₁₋₆ alkyl and C₆₋₁₀aralkyl. Substituents may be present, particularly substituents para to the C═X group when one or more of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, R¹⁶ and R¹⁷ is a phenyl group.

In especially preferred embodiments, R⁴, R⁵, R⁶, or R⁸ are C₁₋₆ alkyl or C₆₋₁₀aralkyl, especially methyl, benzyl or PhCHCH₃.

Compounds of formula (1) where X is represented by NR⁵ or (NR⁶R⁷)⁺Q⁻, include imines or iminium salts. Where a compound of formula (1) is an imine, it may optionally be converted to an iminium salt. Iminium salts are preferred over imines. Preferred iminium salts are represented by compounds of formula (1) in which X is (NR⁶R⁷)⁺Q⁻ such that either R⁶ or R⁷ are hydrogen but that R⁶ and R⁷ are not identical. When the compound of formula (1) is an iminium salt, an anion represented by Q⁻ is present.

Anions which may be represented by Q⁻ include halides, optionally substituted arylsulphonates, such as optionally substituted phenyl and napthyl sulphonates, optionally substituted alkylsulphonates including halogenated alkylsulphonates, such as C₁₋₂₀alkylsulphonates, optionally substituted carboxylates, such as C₁₋₁₀ alkyl and aryl carboxylates, ions derived from the polyhalogenation of boron, phosphorous or antimony, and other common inorganic ions for example perchlorate. Examples of anions which may be present are bromide, chloride, iodide, hydrogen sulphate, tosylate, formate, acetate, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, perchlorate, trifluoromethanesulphonate and trifluoroacetate. Preferred anions include bromide, chloride, iodide, formate and trifluoroacetate, particularly preferred anions include iodide, formate and trifluoroacetate.

In certain preferred embodiments, X is a group of formula (NR⁶R⁷)⁺Q⁻ and R¹ and R⁶ are linked in such a way that when taken together with the carbon atom and the nitrogen atom of the C═X group of the compound of formula (1) that a 5, 6 or 7 membered ring is formed, R⁷ is C₁₋₆ alkyl or C₆₋₁₀aralkyl, especially methyl, benzyl or PhCHCH₃, and R² is optionally substituted hydrocarbyl, preferably C₁₋₆ alkyl, or optionally substituted phenyl especially methoxy, hydroxy or fluoro substituted phenyl. The 5, 6 or 7 membered ring formed by linking R¹ and R⁶ optionally may be fused to another ring system, preferably a benzenoid system which may be substituted, preferred substituents include hydroxy, methoxy and fluoro.

In certain preferred embodiments X is O so that the compound of the formula (I) is a ketone.

Most advantageously, the compound of formula (1) is prochiral, such that the hydrogenated product comprises a chiral atom to which R¹, R² and X are each bonded. Such an asymmetric transfer hydrogenation process forms an especially preferred aspect of the present invention. Most commonly, when the compound of formula (1) is prochiral, R¹ and R² are different, and neither is hydrogen. Advantageously, one of R¹ and R² is aliphatic and the other is aryl or heterocyclyl.

Examples of compounds of formula (1) include acetophenone, 4-chloroacetophenone, 4-methoxyacetophenone, 4-trifluoromethylacetophenone, 4-nitroacetophenone, 2-chloroacetophenone and acetophenone benzylimine.

Further examples of compounds of formula (1) include:

wherein R² and R⁷ are as described above and G¹, G² and G³ are independently hydrogen, chloro, bromo, fluoro, iodo, cyano, nitro, hydroxy, amino, thiol, acyl, hydrocarbyl, perhalogenated hydrocarbyl, heterocyclyl, hydrocarbyloxy, mono or di-hydrocarbylamino, hydrocarbylthio, esters, carbonates, amides, sulphonyl and sulphonamido groups wherein the hydrocarbyl groups are as defined for R¹ above.

Hydrogen donors include hydrogen, primary and secondary alcohols, primary and secondary amines, carboxylic acids and their esters and amine salts, readily dehydrogenatable hydrocarbons, clean reducing agents, and any combination thereof.

Primary and secondary alcohols which may be employed as hydrogen donors comprise commonly from 1 to 10 carbon atoms, preferably from 2 to 7 carbon atoms, and more preferably 3 or 4 carbon atoms. Examples of primary and secondary alcohols which may be represented as hydrogen donors include methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, cyclopentanol, cyclohexanol, benzylalcohol, and menthol. When the hydrogen donor is an alcohol, secondary alcohols are preferred, especially propan-2-ol and butan-2-ol.

Primary and secondary amines which may be employed as hydrogen donors comprise commonly from 1 to 20 carbon atoms, preferably from 2 to 14 carbon atoms, and more preferably 3 or 8 carbon atoms. Examples of primary and secondary amines which may be represented as hydrogen donors include ethylamine, propylamine, isopropylamine, butylamine, isobutylamine, hexylamine, diethylamine, dipropylamine, di-isopropylamine, dibutylamine, di-isobutylamine, dihexylamine, benzylamine, dibenzylamine and piperidine. When the hydrogen donor is an amine, primary amines are preferred, especially primary amines comprising a secondary alkyl group, particularly isopropylamine and isobutylamine.

Carboxylic acids or their esters which may be employed as hydrogen donors comprise commonly from 1 to 10 carbon atoms, preferably from 1 to 3 carbon atoms. In certain embodiments, the carboxylic acid is advantageously a beta-hydroxy-carboxylic acid. Esters may be derived from the carboxylic acid and a C₁₋₁₀ alcohol. Examples of carboxylic acids which may be employed as hydrogen donors include formic acid, lactic acid, ascorbic acid and mandelic acid. The most preferred carboxylic acid is formic acid. In certain preferred embodiments, when a carboxylic acid is employed as hydrogen donor, at least some of the carboxylic acid is preferably present as salt, preferably an amine, ammonium or metal salt. Preferably, when a metal salt is present the metal is selected from the alkali or alkaline earth metals of the periodic table, and more preferably is selected from the group I elements, such as lithium, sodium or potassium. Amines which may be used to form such salts include both aromatic and non-aromatic amines, also primary, secondary and tertiary amines and comprise typically from 1 to 20 carbon atoms. Tertiary amines, especially trialkylamines, are preferred. Examples of amines which may be used to form salts include trimethylamine, triethylamine, di-isopropylethylamine and pyridine. The most preferred amine is triethylamine. When at least some of the carboxylic acid is present as an amine salt, particularly when a mixture of formic acid and triethylamine is employed, the mole ratio of acid to amine is between 1:1 and 50:1 and preferably between 1:1 and 10:1, and most preferably about 5:2. When at least some of the carboxylic acid is present as a metal salt, particularly when a mixture of formic acid and a group I metal salt is employed, the mole ratio of acid to metal ions present is between 1:1 and 50:1 and preferably between 1:1 and 10:1, and most preferably about 2:1. The ratios of acid to salts may be maintained during the course of the reaction by the addition of either component, but usually by the addition of the carboxylic acid.

Readily dehydrogenatable hydrocarbons which may be employed as hydrogen donors comprise hydrocarbons which have a propensity to aromatise or hydrocarbons which have a propensity to form highly conjugated systems. Examples of readily dehydrogenatable hydrocarbons which may be employed by as hydrogen donors include cyclohexadiene, cyclohexene, tetralin, dihydrofuran and terpenes.

Clean reducing agents which may be represented as hydrogen donors comprise reducing agents with a high reduction potential, particularly those having a reduction potential relative to the standard hydrogen electrode of greater than about −0.1 eV, often greater than about −0.5 eV, and preferably greater than about −1 eV. Examples of clean reducing agents which may be represented as hydrogen donors include hydrazine and hydroxylamine.

The most preferred hydrogen donors are propan-2-ol, butan-2-ol, triethylammonium formate and a mixture of triethylammonium formate and formic acid. However, in certain embodiments when the compound of Formula (1) is a protonated imminium salt, it may be desirable to employ a hydrogen donor which is not a carboxylic acid or a salt thereof.

The optionally substituted hydrocarbyl or perhalogenated hydrocarbyl ligand which may be represented by R¹⁸ includes optionally substituted aryl, alkenyl and cyclopentadienyl ligands.

Optionally substituted aryl ligands which may be represented by R¹⁸ may contain 1 ring or 2 or more fused rings which include cycloalkyl, aryl or heterocyclic rings. The ligand may comprise a 6 membered aromatic ring. The ring or rings of the aryl ligand are often substituted with hydrocarbyl groups. The substitution pattern and the number of substituents will vary and may be influenced by the number of rings present, but often from 1 to 6 hydrocarbyl substituent groups are present, preferably 2, 3 or 6 hydrocarbyl groups and more preferably 6 hydrocarbyl groups. Preferred hydrocarbyl substituents include methyl, ethyl, iso-propyl, menthyl, neomenthyl and phenyl. Particularly when the aryl ligand is a single ring, the ligand is preferably benzene or a substituted benzene. When the ligand is a perhalogenated hydrocarbyl, preferably it is a polyhalogenated benzene such as hexachlorobenzene or hexafluorobenzne. When the hydrocarbyl substituents contain enantiomeric and/or diastereomeric centres, it is preferred that the enantiomerically and/or diastereomerically purified forms of these are used. Benzene, p-cymyl, mesitylene and hexamethylbenzene are especially preferred ligands having a 6 membered aromatic ring.

Optionally substituted alkenyl ligands which may be represented by R¹⁸ include C₂₋₃₀, and preferably C₅₋₁₂, alkenes or cycloalkenes with preferably two or more carbon-carbon double bonds, preferably only two carbon-carbon double bonds. The carbon-carbon double bonds may optionally be conjugated to other unsaturated systems which may be present, but are preferably conjugated to each other. The alkenes or cycloalkenes may be substituted preferably with hydrocarbyl substituents. When the alkene has only one double bond, the optionally substituted alkenyl ligand may comprise two separate alkenes. Preferred hydrocarbyl substituents include methyl, ethyl, iso-propyl and phenyl. Examples of optionally substituted alkenyl ligands include cyclo-octa-1,5-diene and 2,5-norbornadiene.

It is however particularly preferred that R¹⁸ is an optionally substituted cyclopentadienyl group.

Optionally substituted cyclopentadienyl group which may be represented by R¹⁸ include particularly ones capable of eta-5 bonding. The cyclopentadienyl group is often substituted with from 1 to 5 hydrocarbyl groups, preferably with 3 to 5 hydrocarbyl groups and more preferably with 5 hydrocarbyl groups. Preferred hydrocarbyl substituents include methyl, ethyl and phenyl. When the hydrocarbyl substituents contain enantiomeric and/or diastereomeric centres, it is preferred that the enantiomerically and/or diastereomerically purified forms of these are used. Examples of optionally substituted cyclopentadienyl groups include cyclopentadienyl, pentamethyl-cyclopentadienyl, pentaphenylcyclopentadienyl, tetraphenylcyclopentadienyl, ethyltetramethylpentadienyl, menthyltetraphenylcyclopentadienyl, neomenthyl-tetraphenylcyclopentadienyl, menthylcyclopentadienyl, neomenthylcyclopentadienyl, tetrahydroindenyl, menthyltetrahydroindenyl and neomenthyltetrahydroindenyl groups. Pentamethylcyclopentadienyl is especially preferred.

It is particularly preferred that R¹⁸ is an optionally substituted cyclopentadienyl group.

When either A or B is an amide group represented by —NR¹⁹—, —NHR¹⁹, NR¹⁹R²⁰, —NR²³—, —NHR²³ or NR²²R²³ wherein R²⁰ and R²¹ are as hereinbefore defined, and where R¹⁹ or R²³ is an acyl group represented by —C(O)R²¹ or —C(O)R²⁴, R²¹ and R²⁴ independently are often linear or branched sulphonated C₁₋₇alkyl, sulphonated C₁₋₈-cycloalkyl or sulphonated aryl, for example sulphonated phenyl. Examples of sulphonated acyl groups which may be represented by R¹⁹ or R²³ include sulphonated benzoyl, acetyl and halogenoacetyl groups.

When either A or B is present as a sulphonamide group represented by —NR¹⁹—, —NHR¹⁹, NR¹⁹R²⁰, —NR²³—, —NHR²³ or NR²²R²³ wherein R²⁰ and R²² are as hereinbefore defined , and where R¹⁹ or R²³ is a sulphonyl group represented by —S(O)₂R²¹ or —S(O)₂R²⁴, R²¹ and R²⁴ independently are often linear or branched sulphonated C₁₋₈alkyl, sulphonated C₁₋₈cycloalkyl or sulphonated aryl, for example sulphonated phenyl. Preferred sulphonyl groups include sulphoanted derivatives of methanesulphonyl, trifluoromethanesulphonyl and especially phenylsulphonyl groups and naphthylsulphonyl groups.

When either of A or B is present as a group represented by —NR¹⁹—, —NHR¹⁹, NR¹⁹R²⁰, —NR²³—, —NHR²³ or NR²²R²⁴ wherein R²⁰ and R²³ are as hereinbefore defined, and where R¹⁹ or R²³ is a group represented by C(O)NR²¹R²⁵, C(S)NR²¹R²⁵, C(═NR²⁵)SR²⁶, C(═NR²⁵)OR²⁶, C(O)NR²⁴R²⁷, C(S)NR²⁴R²⁷, C(═NR²⁷)SR²⁸ or C(═NR²⁷)OR²⁸, R²¹ and R²⁴ independently are often linear or branched sulphonated C₁₋₈alkyl, such as methyl, ethyl, isopropyl, C₁₋₈cycloalkyl or sulphonated aryl, for example phenyl, groups and R²²⁻²⁵ are often each independently hydrogen or linear or branched C₁₋₈alkyl, such as methyl, ethyl, isopropyl, sulphonated C₁₋₈cycloalkyl or aryl, for example phenyl, groups.

When B is present as a group represented by —OR²², —SR²², —PR²²— or —PR²²R²⁴, R²² and R²⁴ independently are often linear or branched C₁₋₈alkyl, such as methyl, ethyl, isopropyl, C₁₋₈cycloalkyl or aryl, for example phenyl.

It will be recognised that the precise nature of A and B will be determined by whether A and/or B are formally bonded to the metal or are coordinated to the metal via a lone pair of electrons.

It is particularly preferred in accordance with the invention that A is a group of the formula —NHR¹⁹ or —NR¹⁹— where R¹⁹ is represented by the group —SO₂R²¹ in which R²¹ is an optionally substituted sulphonated hydrocarbyl group, sulphonated perhalogenated hydrocarbyl group or optionally substituted sulphonated heterocyclyl group. Most preferably R²¹ is a sulphonated phenyl group having n sulphonate groups where n is 1 to 5. When n is 1 to 4 the sulphonate groups may be present in any substitution pattern on the aromatic ring. In the particular case where n=1 then the sulphonate group may be ortho, meta or para to the sulphonamide group.

B is preferably-NH₂ or —NH—.

The groups A and B are connected by a linking group E. The linking group E achieves a suitable conformation of A and B so as to allow both A and B to bond or coordinate to the metal, M. A and B are commonly linked through 2, 3 or 4 atoms. The atoms in E linking A and B may carry one or more substituents. The atoms in E, especially the atoms alpha to A or B, may be linked to A and B, in such a way as to form a heterocyclic ring, preferably a saturated ring, and particularly a 5, 6 or 7-membered ring. Such a ring may be fused to one or more other rings. Often the atoms linking A and B will be carbon atoms. Preferably, one or more of the carbon atoms linking A and B will carry substituents in addition to A or B. Substituent groups include those which may substitute R¹, as defined above. Advantageously, any such substituent groups are selected to be groups which do not coordinate with the metal, M. Preferred substituents include halogen, cyano, nitro, sulphonyl, hydrocarbyl, perhalogenated hydrocarbyl and heterocyclyl groups as defined above. Most preferred substituents are C₁₋₆ alkyl groups, and phenyl groups. Most preferably, A and B are linked by two carbon atoms, and especially an optionally substituted ethyl moiety. When A and B are linked by two carbon atoms, the two carbon atoms linking A and B may comprise part of an aromatic or aliphatic cyclic group, particularly a 5, 6 or 7-membered ring. Such a ring may be fused to one or more other such rings. Particularly preferred are embodiments in which E represents a 2 carbon atom separation and one or both of the carbon atoms carries an optionally substituted aryl group as defined above or E represents a 2 carbon atom separation which comprises a cyclopentane or cyclohexane ring, optionally fused to a phenyl ring.

E preferably comprises part of a compound having at least one stereospecific centre. Where any or all of the 2, 3 or 4 atoms linking A and B are substituted so as to define at least one stereospecific centre on one or more of these atoms, it is preferred that at least one of the stereospecific centres be located at the atom adjacent to either group A or B. When at least one such stereospecific centre is present, it is advantageously present in an enantiomerically purified state.

When B represents —O— or —OH, and the adjacent atom in E is carbon, it is preferred that B does not form part of a carboxylic group.

Sulphonated compounds which may be represented by A—E—B, or from which A—E—B may be derived by deprotonation, are often aminoalcohols or diamines in which an or the amino nitrogen atom has bound (directly or indirectly) thereto a substituent incorporating a group R²⁰ to R²² or R²⁴ to R²⁸ in the form of an optionally substituted sulphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group or an optionally substituted sulphonated heterocyclyl group. Examples of aminoalcohols from which said N-substituted compound may be derived including 4-aminoalkan-1-ols, 1-aminoalkan-4-ols, 3-aminoalkan-1-ols, 1-aminoalkan-3-ols, and especially 2-aminoalkan-1-ols, 1-aminoalkan-2-ols, 3-aminoalkan-2-ols and 2-aminoalkan-3-ols, and particularly 2-aminoethanols or 3-aminopropanols. Further aminoalcohols are 2-aminocyclopentanols and 2-aminocyclohexanols, preferably fused to a phenyl ring. Examples of diamines from which said N-substituted compounds may be derived include 1,4-diaminoalkanes, 1,3-diaminoalkanes, especially 1,2- or 2,3-diaminoalkanes and particularly ethylenediamines. Further diamines are 1,2-diaminocyclopentanes and 1,2-diaminocyclohexanes, preferably fused to a phenyl ring. The aminoalcohols or diamines are advantageously substituted, especially on the linking group, E, by at least one alkyl group, such as a C₁₋₄-alkyl, and particularly a methyl, group or at least one aryl group, particularly a phenyl group.

In summary it is particularly preferred that E has two carbon atoms linking A and B, one or both of these atoms being optionally substituted. In certain preferred embodiments E is of the formula —CHR³⁰—CHR³¹— where R³⁰ and R³¹ are independently hydrogen or an optionally substituted hydrocarbyl group.

In other preferred embodiments, E is a carbon-carbon bond that is part of an optionally substituted cycloaliphatic ring, preferably cyclopentyl or cyclohexyl.

Examples of ligands from which compounds A—E—B may be derived are as follows:

in which:

W is —OH or —NH₂;

R³² is an aryl group having at least one —SO₃H or SO₃M¹ (M¹=alkali metal) substituent and is further optionally substituted, e.g. with a carboxylic acid group which may, for example, be ortho to the —SO₃H or —SO₃M¹ group and may lead to anhydride formulation therewith. More preferably R³² is a phenyl group having one —SO₃H or —SO₃M¹ substituent; and

R³³, R³⁴ are independently optionally substituted hydrocarbyl groups or R³³ and R³⁴ are optionally linked in such a way as to define an optionally substituted ring, more preferably R³³ and R³⁴ are independently phenyl or R³³ and R³⁴ are linked so as to define a cyclohexyl ring.

Specific examples of aminoalcohols and diamines from which the sulphonated compounds A—E—B may be derived are:

Advantageously, certain ligands are prepared by oxidative cleavage of the corresponding di-sulphide.

Accordingly there is provided a process comprising reacting a di-sulphide of formula:

with an oxidant to produce a compound of formula:

wherein:

W is —OH or —NH₂;

R³² is an aryl group having at least one —SO₃H or SO₃M¹ (M¹=alkali metal) substituent;

R³⁵ is an aryl group; and

R³³, R³⁴ are independently optionally substituted hydrocarbyl groups or R³³ and R³⁴ are optionally linked in such a way as to define an optionally substituted ring, more preferably R³³ and R³⁴ are independently phenyl or R³³ and R³⁴ are linked so as to define a cyclohexyl ring.

Preferably the substitution pattern of the aryl group R³² is such that the —SO₃H or SO₃M¹ (M¹=alkali metal) substituent is positioned para with respect to the SO₂NH—CHR³⁴—CHR³³—W group. Corresponding a similar substitution pattern in R³⁵ is preferred.

Preferably the oxidant is alkaline hydrogen peroxide, particularly a mixture is sodium hydroxide solution and hydrogen peroxide solution.

Metals which may be represented by M include metals which are capable of catalysing transfer hydrogenation. Preferred metals include transition metals, more preferably the metals in Group VIII of the Periodic Table, especially ruthenium, rhodium or iridium. When the metal is ruthenium it is preferably present in valence state II. When the metal is rhodium or iridium it is preferably present in valence state I.

Anionic groups which may be represented by Y include hydride, hydroxy, hydrocarbyloxy, hydrocarbylamino and halogen groups. Preferably when a halogen is represented by Y, the halogen is chloride. When a hydrocarbyloxy or hydrocarbylamino group is represented by Y, the group may be derived from the deprotonation of the hydrogen donor utilised in the reaction.

Basic ligands which may be represented by Y include water, C₁₋₄ alcohols, C₁₋₈ primary or secondary amines, or the hydrogen donor which is present in the reaction system. A preferred basic ligand represented by Y is water.

Most preferably, the nature of A—E—B, R¹⁸ and Y are chosen such that the catalyst is chiral. When such is the case, an enantiomerically and/or diastereomerically purified form is preferably employed. Such catalysts are most advantageously employed in asymmetric transfer hydrogenation processes. In many embodiments, the chirality of the catalyst is derived from the nature of A—E—B.

The process is carried out preferably in the presence of a base, especially when Y is not a vacant site. The pK_(a) of the base is preferably at least 8.0, especially at least 10.0. Convenient bases are the hydroxides, alkoxides and carbonates of alkali metals; tertiary amines and quaternary ammonium compounds. Preferred bases are sodium 2-propoxide and triethylamine. When the hydrogen donor is not an acid, the quantity of base used can be up to 5.0, commonly up to 3.0, often up to 2.5 and especially in the range 1.0 to 3.5, by moles of the catalyst. When the hydrogen donor is an acid, the catalyst may be contacted with a base prior to the introduction of the hydrogen donor. In such a case, the mole ratio of base to catalyst prior to the introduction of the hydrogen donor is often from 1:1 to 3:1, and preferably about 1:1.

Although gaseous hydrogen may be present, the process is normally operated in the absence of gaseous hydrogen since it appears to be unnecessary.

Advantageously, the process is carried out in the substantial absence of carbon dioxide.

When the product(s) from dehydrogenation of the hydrogen donor is volatile, for example boils at under 100° C., the removal of this volatile product is preferred. The removal can be accomplished by distillation preferably at less than atmospheric pressure or by use of inert gas sparging. When reduced pressure distillation is employed, the pressure is often no more than 500 mmHg, commonly no more than 200 mmHg, preferably in the range of from 5 to 100 mmHg, and most preferably from 10 to 80 mmHg. When the product(s) from dehydrogenation of the hydrogen donor is a gaseous material, for example when formic acid is present as a hydrogen donor, the removal is most preferably accomplished by the use of inert gas sparging, with for example nitrogen.

Suitably the process is carried out at temperatures in the range of from minus 78 to plus 150° C., preferably from minus 20 to plus 110° C. and more preferably from minus 5 to plus 60° C. The initial concentration of the substrate, a compound of formula (1), is suitably in the range 0.05 to 1.0 and, for convenient larger scale operation, can be for example up to 6.0 more especially 0.25 to 2.0, on a molar basis. The molar ratio of the substrate to catalyst is suitably no less than 50:1 and can be up to 50000:1, preferably between 100:1 and 5000:1 and more preferably between 200:1 and 2000:1. The hydrogen donor is preferably employed in a molar excess over the substrate, especially from 5 to 20 fold or, if convenience permits, greater, for example up to 500 fold. After reaction, the mixture is worked up by standard procedures.

During the reaction a solvent may be present, preferably a polar solvent, more preferably a polar aprotic solvent, for example acetonitrile, dimethylformamide or dichloromethane. Conveniently, the hydrogen donor may be the solvent when the hydrogen donor is liquid at the reaction temperature, or it may be used in combination with a diluent. Usually it is preferred to operate in substantial absence of water, but water does not appear to inhibit the reaction. If the hydrogen donor or the reaction solvent is not miscible with water and the desired product is water soluble, it may be desirable to have water present as a second phase extracting the product, pushing the equilibrium and preventing loss of product optical purity as the reaction proceeds. The concentration of substrate may be chosen to optimise reaction time, yield and enantiomeric excess.

The catalytic species is believed to be substantially as represented in the above formula. It may be employed as an oligomer or metathesis product, on a solid support or may be generated in situ.

The catalyst can be made by reacting a metal aryl or alkenyl halide complex with a compound of formula A—E—B as defined above or a protonated equivalent from which it may be derived, and, where Y represents a vacant site, reacting the product thereof with a base. The metal aryl or alkenyl halide complex preferably has the formula [MR¹⁸Z₂]₂ when M is ruthenium (II) and has the formula [MR¹⁸Z]₂ when M is iridium or rhodium (I), wherein R¹⁸ is as defined above, and Z represents a halide, particularly chloride.

For the preparation of the catalysts according to the present invention, a solvent is preferably present. Suitable reaction temperatures are in the range 0–100° C., for example 20–70° C., often giving reaction times of 0.5–24.0 h. After reaction is complete, the catalyst may if desired be isolated, but is more conveniently stored as the solution or used soon after preparation. The solution can contain the hydrogen donor and this, if a secondary alcohol, may be present in or used as the solvent for step (a) and/or (b). The preparation and after-handling should preferably be under an inert atmosphere, and particularly in carbon dioxide and oxygen-free conditions.

The catalyst or catalyst solution is generally treated with base either just prior to use in a transfer hydrogenation reaction, or during use. This can be accomplished by adding base to the catalyst in solution, or to the compound of formula (1) in solution, or by addition to the transfer hydrogenation reaction. Iminium salts can generally be obtained by known literature methods, for example the quaternisation of imines, such as by treatment of imines with alkylating agents. Transfer hydrogenation can be accomplished by transferring the solution of catalyst to a solution of substrate, a compound of general formula I. Alternatively a solution of substrate can be added to a solution of catalyst. Base may be pre-added to the catalyst solution and/or the substrate solution, or can be added later. The hydrogen donor if not already present in the catalyst solution may be added to the substrate solution, or may be added to the reaction mixture.

The invention is illustrated by the following Examples.

The invention will be illustrated by the following non-limiting Examples. For convenience, the Examples are divided into two sections, viz a Ligand Synthesis Section in which Examples LS1–4 and LS18 describe the synthesis of various ligands embraced by the formula A—E—B described above and a “Catalyst Preparation and Hydrogenation” Section in which Examples TH5–17 and describe preparation of catalysts with ligands as synthesised in Examples LS1–4 and transfer hydrogenation reactions employing these catalysts. Example TH19 describes a transfer hydrogenation process wherein the catalyst is removed at he end of reaction by treatment with ion exchange resins.

EXAMPLES Example LS 1 Preparation of Sodium (1S, 2S)-1,2-diphenylethylenediamine-N-phenylsulfonyl-4-sulfonate (CB 3.016)

(i) Synthesis of Sodium 4,4′-dithiobisbenzenesulfonate. (CB3.011)

Sodium 4,4′-dithiobisbenzenesulfonate (CB3.011) was synthesised following the protocol of Smith et. al (H. A Smith, G. Goughty, G Dorin j. Chem. Soc., 1964, 29, 1484–1488) with some minor modifications. Sulfanilic acid (47.5 g, 0.25 mol) and anhydrous sodium carbonate were dissolved in water (500 ml) by warming. The solution was cooled to 15° C. and sodium nitrite (18.5 g, 0.27 mol) in water (50 ml) was added. The mixture was poured slowly into conc. hydrochloric acid (52.5 ml, 0.64 mol) and crushed ice (300 g) and the resulting suspension was stirred for 15 minutes.

Sodium sulfide nonahydrate (65 g, 0.27 mol) and powdered sulfur (8.5 g, 0.27 mol) were dissolved in water (75 ml) at 100° C. A solution of sodium hydroxide (10 g, 0.25 mol) in water (100 ml) was added and the resulting disodium disulfide solution was cooled to 0° C. (ice bath). The diazo solution was added over a period of 30 minutes, along with 50 g of ice to keep the temperature below 5° C. The ice bath was removed and the reaction mixture was allowed to come to room temperature. After 2 hours the evolution of nitrogen ceased and the reaction mixture was acidified to pH 2 by addition of conc. hydrochloric acid. The precipitated sulfur was filtered off and the solution was concentrated by heating on a stirrer hotplate to a volume of ca. 500 ml. After cooling to r.t. the solution was neutralised with sodium hydroxide solution (10% in water) and concentrated to 400 ml. The product crystalised after standing overnight at r.t. and was collected in a buchner funnel and dried under high vacuum. Yield 19.8 g (37.5%, 46.9 mmol). ¹H NMR (400 MHz, D₂O) d 7.36 (d, J=8.2 Hz, 4H), 7.53 (d, J=8.2 Hz, 4H); ¹³C NMR (100 MHz, D²O) d 126.47 (+), 127.04 (+), 140.07 (C_(quart)), 141.38 (C_(quart)).

(ii) Synthesis of 4,4′-Disulfanediyl-bis-benzene sulfonyl chloride. (CB3.012)

A flask (100 ml) with reflux condenser and a bubbler was charged with CB3.011 (10 g, 23.7 mmol), POCl₃ (10 ml) and PCl5 (5 g). The mixture was heated to reflux for 2 hours (120° C. oil bath temperature). After cooling to room temperature temperative dichloromethane (50 ml) was added and the resulting mixture was poured into ice. After 1 hour of intensive stirring the organic layer was separated and stirred with conc. bicarbonate solution (100 ml) for another hour. The organic layer was separated again, dried over sodium sulfate and concentrated to a volume of ca. 25 ml. The product was precipitated by slow addition of cyclohexane with stirring, filtered off and dried under high vacuum. Yield 6.89 g (16.6 mmol, 70%). m.p. 139° C. (Lit.^(Ref1): 142° C.); ¹H NMR (400 MHz, CDCl₃) d 7.69 (d, J=8.6 Hz, 4H), 7.98 (d, J=8.6 Hz, 4H); ¹³C NMR (100 MHz, CDCl₃) d 126.69 (+), 128.08 (+), 143.03 (C_(quart)), 145.05 (C_(quart)); MS (+FAB(3-NBA)) m/e 413.9 (100, M).

(Ref 1: T. Zincke, W. Frohneberg Chem Ber., 1909, 42, 2721–2736)

(iii) Synthesis of (CB3.010)

To a solution of (S,S)-diphenylethylenediamine (3.73 g, 17.6 mmol) and triethylamine (5 ml) in 50 ml of dichloromethane a solution of 4,4′-Disulfanediyl-bis-benzenesulfonyl chloride (CB3.012) (3.32 g, 8.0 mmol) in dichloromethane (10 ml) was added slowly at 0° C. (ice-bath). The reaction mixture was stirred for 12 hours at room temperature and then concentrated under reduced pressure. The crude product was purified by chromatography on silica (first DCM, then DCM/methanol 25:1 as eluent). The product was obtained as a slightly yellow solid. Yield 5.65 g (7.37 mmol, 92%). m.p. 108–110° C.; ¹H NMR (400 MHz, CDCl₃) d 4.16 (d, J=5.3 Hz, 2H), 4.44 (d, J=5.3 Hz, 2H), 7.07–7.14 (m, 20H), 7.20 (d, J=8.8 Hz, 4H), 7.35 (d, J=8.8 Hz, 4H); ¹³C NMR (100 MHz, CDCl₃) d 60.61 (+), 63.73 (+), 126.18 (+), 126.80 (+), 127.20 (+), 127.66 (+), 127.72 (+), 127.81 (+), 128.48 (+), 128.64 (+), 138.92 (C_(quart)), 139.29 (C_(quart)), 141.05 (C_(quart)), 141.12 (C_(quart)); MS (+FAB(3-NBA)) m/e 767 (47, M+1), 106 (100); [a]D²⁰ −87.0° (=1.31, EtOH).

(iv) Synthesis of Sodium (1S, 2S)-1,2-diphenylethylenediamine-N-phenylsulfonyl-4-sulfonate (CB3.016)

CB3.016: Sodium hydroxide solution (10 ml, 2.5M in water, 25 mmol) and hydrogen peroxide solution (5 ml, 27.5% by weight in water) were added a solution of CB3.010 (4.82 g, 6.28 mmol) in methanol (50 ml). An exothermic reaction resulted. The resulting mixture was stirred for 2 hours before another 2 ml or hydrogen peroxide solution were added. Stirring at room temperature was continued for 12 hours, then concentrated sodium hydrogen sulfite solution was added (10 ml) and the mixture was stirred for another 2 hours. The reaction mixture was concentrated to dryness under reduced pressure, water (50 ml) was added to dissolve the inorganic salts and the product was filtered off. The product was washed with cold water (100 ml) and dichloromethane (50 ml) and dried under high vacuum. Yield 4.454 g (10.3 mmol, 82%). m.p.>280° C. (dec.); ¹H NMR (400 MHz, DMSO-d₆) d 4.43 (d, J=10.4 Hz, 1H), 4.65 (d, J=10.4 Hz, 1H), 6.79–6.93 (m, 5H), 7.19 (s, 5H), 7.41 (d, J=8.6 Hz, 2H), 7.45 (d, J=8.6 Hz, 2H), 8.61 (bs, 4); ¹³C NMR (100 MHz, DMSO-d₆) d 59.24 (+), 62.10 (+), 126.35 (+), 126.72 (+), 128.25 (+), 128.39 (+), 128.93 (+), 129.02 (+), 129.40 (+), 134.61 (C_(quart)), 136.14 (C_(quart)), 141.05 (C_(quart)), 152.03 (C_(quart)); MS (FAB(3-NBA)) m/e 433.1 (93, M+1), 165.0 (100); [a]_(D) ²⁰ −76.9° (c=1.3, DMSO).

Example LS2 Preparation of Sodium (1R, 2R)-1,2-diaminocyclohexyl-N-phenylsulfonyl-4-sulfonate (CB3.019)

(i) Synthesis of CB 3.018

To solution of (R,R)-1,2-diaminocyclohexane (1.76 g, 15.4 mmol) and triethylamine (5 ml) in 50 ml of dichloromethane was added slowly a solution of 4,4′-Disulfanediyl-bis-benzenesulfonyl chloride (CB3.012) (2.91 g, 7.0 mmol) in dichloromethane (10 ml) at −78° C. (acetone/dry ice bath). The reaction mixture was allowed to warm up to room temperature stirred for 12 hours at this temperature and then concentrated under reduced pressure. The crude product was purified by chromatography on silica (first DCM, then DCM/methanol 5:1 as eluent). The product was obtained as a slightly yellow solid. Yield 3.44 g (6.02 mmol, 86%). m.p. 125–128° C.; ¹H NMR (400 MHz, CD₃OD) d 1.01–1.34 (m, 10H), 1.53–1.65 (m, 4H), 1.86–1.98 (m, 2H), 2.35–2.45 (m, 2H), 2.74–2.82 (m, 2H, 7.69 (d, J=8.6 Hz, 4H), 7.84 (d, J=8.6 Hz, 4H); ¹³C NMR (100 MHz, CD₃OD) d 25.49 (−), 26.13 (−), 33.05 (−), 33.79 (−), 55.77 (+), 60.31 (+), 127.84 (+), 128.70 (+), 141.94 (C_(quart)), 142.62 (C_(quart)); MS (FAB(3-NBA)) m/e 571 (100, M+1); [a]D²⁰ +36.5° (c=2.0, EtOH).

(ii) Synthesis of Sodium (1R, 2R)-1,2-diaminocyclohexyl-N-phenylsulfonyl-4-sulfonate (CB3.019)

Sodium hydroxide solution (4 ml, 1M in water, 4 mmol) and hydrogen peroxide solution (2 ml, 27.5% by weight in water) were added to a solution of CB3.018 (1.142 g, 2.0 mmol) in methanol (20 ml). An exothermic reaction ensued. The resulting mixture was stirred for 2 hours before another 2 ml hydrogen peroxide solution were added. Stirring at room temperature was continued for 12 hours, then concentrated sodium hydrogen sulfite solution was added (5 ml) and the mixture was stirred for another 2 hours. The reaction mixture was concentrated to dryness under reduced pressure, water (20 ml) was added to dissolve the inorganic salts and the product was filtered off. The product was washed with cold water (40 ml), ethanol (20 ml), dichloromethane (50 ml) and dried under high vacuum. Yield 883 mg (2.64 mmol, 66%). m.p.>300° C.; ¹H NMR (400 MHz, DMSO-d₆) d 0.90–1.38 (m, 7H), 1.84–1.98 (m, 1H), 2.66-2.82 (m, 1H), 2.88–3.02 (m, 1H), 7.82 (s, 4H), 7.89 (bs, 4H); ¹³C NMR (100 MHz, DMSO-d₆) d 23.80 (−), 24.69 (−), 29.95 (−), 31.21 (−), 54.22 (+), 55.62 (+), 126.90 (+), 127.17 (+), 142.00 (C_(quart),) 152.54 (C_(quart)), MS (−FAB(3-NBA)) m/e 333 (100, M−1); [a]D₂₀ +21.5° (c=1.7, DMSO).

Example LS3 Preparation of Sodium (1S, 2S)-1,2-diphenylethylenediamine-N-phenylsulfonyl-2-sulfonate (3.022)

Benzene-1,2-disulfonic acid anhydride (1.30 g, 5.9 mmol) was added to a solution of (S,S)-diphenylethylenediamine (1.25 g, 5.9 mmol) in 150 ml of dichloromethane at room temperature. The reaction mixture was stirred for 1 hour and then concentrated under reduced pressure. Isopropanol (50 ml) was added to the residue and the mixture heated to reflux for 15 minutes. After cooling to room temperature the product precipitated and was collected in a sinter-funnel and washed with isopropanol (50 ml). The product is dried under high vacuum at 60° C. for 12 hours. Yield 1.96 g (4.54 mmol, 77%). m.p.>250° C.; ¹H NMR (400 MHz, d6-DMSO) d 4.60 (d, J=11.9 Hz, 1H), 4.69 (dd, J=11.9, 8.2 Hz, 1H), 6.71–6.79 (m, 5H), 7.12 (dt, J=7.8, 1.2 Hz, 1H), 7.16–7.19 (m, 5H), 7.35 (dt, J=7.8, 1.2 Hz, 1H), 7.43 (dd, J=7.8, 1.2 Hz, 1H), 7.43 (dd, J=7.8, 1.2 Hz, 1H), 7.83 (dd, J=7.8, 1.2 Hz, 1H), 8.66 (s, 3H), 8.88 (d, J=8.2 Hz, 1H); ¹³C NMR (100 MHz, d6-DMSO) d 60.61 (30 ), 63.73 (+), 126.18 (+), 126.80 (+), 127.20 (+), 127.66 (+), 127.72 (+), 127.81 (+), 128.48 (+), 128.64 (+), 138.92 (C_(quart)), 139.29 (C_(quart)), 141.05 (C_(quart)), 141.12 (C_(quart)); MS (+FAB(3-NBA)) m/e 767 (47, M+1), 106 (100); [a]D²⁰ −87.0° (c=1.31, EtOH).

Example LS4 Synthesis of Sodium (1R, 2R)-1 ,2-diphenylethylenediamine-N-phenylsulfonyl-4-sulfonate (TT-CB4)

The preparation of TT-CB4 was undertaken in an identical manner to CB3.016 (Example LS1) but using R,R-diphenylethylenediamine in place of S,S-diphenylethylenediamine.

Catalyst Preparation and Hydrogenation Section.

Unless otherwise stated, the following procedures were employed for each of Examples TH5–TH19 below.

(a) Catalyst Preparation

In a Schlenk flask (25 ml) with a magnetic stirring-bar a solution of KOt-Bu in isopropanol (0.8 ml of a 0.1 M solution, 0.08 mmol) was added to a suspension of ligand (0.08 mmol) in water (1 ml) and stirred under N₂-atmosphere at room temperature until a clear solution was obtained. To this solution the transition metal compound (0.01 mmol) was added and the mixture stirred under an argon atmosphere at 40° C. for two hours.

(b) Hydrogenation

After cooling of the solution obtained in (i) to 22° C. the substrate to be hydrogenated (2 mmol) in isopropanol (10 ml) and KOt-Bu in isopropanol (2.0 ml of a 0.1 M solution, 0.20 mmol) were added to start the reaction.

Samples were taken out of the reaction mixture at various times and analysed by gas chromatography (β-dex column).

The ligand, transition metal compound and hydrogenation substrate used are tabulated below for each Example together with the results obtained in the hydrogenation reaction.

Example TH5

This Example demonstrates ruthenium catalysed asymmeteric transfer hydrogenation of acetophenone in accordance with the equation:

The reagents used were as follows

Transition Metal [RuCl₂(p-cymene)]₂  6.1 mg Compound Ligand CB3.016 34.6 mg Hydrogenation Substrate Acetophenone  240 mg

The results are shown in Table 1.

TABLE 1 Ruthenium/CB3.016/acetophenone. Hydrogenation at 22° C. Time [h] T [° C.] Conversion [%] ee [%]  3 22 16 95.0 20 22 61 95.3 28 22 74 95.3 44 22 96 94.4

Example TH6

Example TH5 was repeated save that in step (a) stirring was effected at 22° C. (rather than 40° C.) and that step (b) was carried out at temperatures of 22° C., 30° C. and 40° C.

The results are shown in Tables 2 to 4.

TABLE 2 Ruthenium/CB3.016/Acetophenone Hydrogenation at 22° C. Time [h] T [° C.] Conversion [%] ee [%] 1 22 3 — 2 22 7 — 3 22 10 — 4 22 13 — 16 22 39 96.3 25 22 51 95.3 41 22 58 96.3 69.5 22 62 96.0

TABLE 3 Ruthenium/CB3.016/Acetophenone at 30° C. Time [h] T [° C.] Conversion [%] ee [%] 1 30 10 95.0 2 30 19 — 3 30 26 — 4 30 34 95.7 16 30 68 95.2 25 30 73 95.5 41 30 77 95.1 69.5 30 77 94.2

TABLE 4 Ruthenium/CB3.016/Acetophenone at 40° C. Time [h] T [° C.] Conversion [%] ee [%] 1 40 31 95.2 2 40 48 94.4 3 40 58 95.6 4 40 66 94.6 16 40 89 94.2 25 40 90 93.7 41 40 92 93.5 69.5 40 91 93.4

The temperature-effect is significant, but in all cases a slowdown or standstill of the reaction after about 20 h was observed, probably due to precipitation of the catalyst.

The drop in enantioselectivity was not as high as expected.

Example TH7

This Example demonstrates the rhodium catalysed transfer hydrogenation of acetophenone using CB3.016 as a ligand for the catalyst.

The following reactants were employed.

Transition Metal Compound ¹Rh(Cp*)Cl₂]₂ Ligand CB3.016 Hydrogenation Substrate Acetophenone ¹[Rh(pentamethylcyclodienyl)Cl₂]₂

The results obtained are shown in Table 5.

TABLE 5 Rhodium/CB3.016/Acetophenone Time [h] T [° C.] Conversion [%] ee [%]  1 22 34 97 18 22 72 97

Example TH8

This Example demonstrates the ruthenium catalysed transfer hydrogenation of acetophenone using CB3.019 as catalyst ligand.

The following reactants were used.

Transition Metal Compound [RuCl₂(p-cymene)]₂ Ligand CB3.019 Hydrogenation Substrate Acetophenone The results are shown in Table 6

TABLE 6 Ruthenium/CB3.019/Acetophenone Time [h] Conversion [%] ee [%] 1  1 — 19.5 28 88.0 28 40 90.7 51 54 90.8 96 67 89.8

Example TH9

This Example demonstrates the rhodium catalysed transfer hydrogenation of acetophenone using CB3.019 as catalyst ligand.

The following reactants were used.

Transition Metal Compound [Rh(Cp*)Cl₂]₂ Ligand CB3.019 Hydrogenation Substrate Acetophenone The results are shown in Table 7

TABLE 7 Rhodium/CB3.019/Acetophenone. Time [h] Conversion [%] ee [%] 1 62 97.6 19.5 94 94.9 28 94 94.5 51 94 94.6 96 96 94.5

Comparing the results of Examples TH8 and TH9, the rhodium-catalysed system proved to be more reactive and selective compared to the ruthenium one. The enantioselectivity was close to 98% after 1 h and dropped slightly at the end to 94.5%.

Example TH10

This Example investigates the use of a catalysts based on ruthenium and either CB3.016, CB3.019 or CB.022 in the hydrogenation of a range of aromatic ketones as hydrogenation substrate. The hydrogenation procedure used was as described previously save that 1 cm³ of water was added additionally to the isopropanol and KOt-By. The water concentration was thus 15%.

The following reactants were used

Transition Metal Compound [RuCl₂(p-cymene)]₂ Ligand (1) CB3.016 Ligand (2) CB-3.019 Ligand (3) CB3.022 Hydrogenation Substrate (5)–(10) See below

The results are shown in Table 8.

TABLE 8 Ruthenium/CB3.016(1) or CB3.019(2) or CB3.022(3)/Ketones(5)–(10). Reaction time Conversion Ketone Ligand [h] [%] Ee [%] 5 1 48 96 94 5 2 48 91 88 5 3 48 11 91 6 1 4 100 81 6 2 4 100 88 7 1 24 90 87 7 2 24 91 81 8 1 18 10 24 8 2 18 18 55 9 1 42 31 91 9 2 42 35 83 10 1 72 94 95 10 2 48 87 90

Example TH11

Example TH10 was repeated but using [Rh(Cp*)Cl₂]₂ as the transition metal compound. Thus, the reactants were as follows:

Transition Metal Compound [Rh(Cp*)Cl₂]₂ Ligand (1) TT-CB4 Ligand (2) CB3.019 Hydrogenation Substrate (5)–(10) See above

The results are shown in Table 9.

TABLE 9 Rhodium/TT-CB4(1) or CB3.019(2)/Ketones(5)–(10) Reaction time Conversion Ketone Ligand [h] [%] ee [%] 5 1 24 92 97 5 2 18 94 95 6 1 4 100 83 6 2 2 100 88 7 1 18 98 95 7 2 4 99 94 8 1 18 2 22 8 2 18 40 76 9 1 42 9 94 9 2 42 65 95 10 1 64 81 82 10 2 48 95 96

The results in tables 8 and 9 show the effectiveness of TT-CB4 and CB3.019 in transfer hydrogenations. p-Trifluoromethyl acetophenone (6) reacts rapidly and quantitatively giving moderate and very similar ee's in the ruthenium and rhodium catalysed reaction. m-Trifluoromethyl acetophenone (7) reacts slightly more slowly giving a very high ee only in the rhodium catalysed reaction. o-Trifluoromethyl acetophenone (8) reacts very slowly, compared to (6) and (7). Only the rhodium-catalysed reaction using ligand (2) shows moderate enantioselectivity. The electron-rich p-methoxy acetophenone (9) reacts relatively slowly, as expected. It was not possible to obtain a conversion above 65% under these conditions. 2-Acetylnaphthalene (10) reacts similarly to acetophenone.

Example TH12

The Example demonstrates the ruthenium catalysed transfer hydrogenation of acetophenone using TT-CB4 as catalyst ligand.

Transition Metal Compound [RuCl₂(p-cymene)]₂ Ligand TT-CB4 Hydrogeneration Substrate Acetophenone

The results are shown in Table 10.

TABLE 10 Ruthenium/TT-CB4/Acetophenone Reaction Time (hours) Conversion *(%) Enantiomeric excess (%) 19 30 94.4 24.5 34 95.0 42.5 46 94.4 49 48 94.2 66 55 94.4 73 58 94.3 90 62 94.4 96 64 94.4

Example TH13

Example TH12 was repeated using 4-Bromoacetophenone as hydrogenation substrate in place of acetophenone.

The following reactants were employed.

Transition Metal Compound [RuCl₂(p-cymene)]₂ Ligand TT-CB4 Hydrogenation Substrate 4-Bromoacetophenone

The results shown in Table 11

TABLE 11 Ruthenium/TT-CB4/4-Bromoacetophenone Reaction Time (hours) Conversion (%) Enantiomeric excess (%) 20.5 43 92.4 27 51 92.4 44 67 92.3 50.5 73 92.4 67.5 82 92.3 73.5 85 92.3 139 98 92.1

Example TH14

Example TH13 was repeated but using 2-Fluoroacetophenone as hydrogenation substrate.

The following reactants were employed.

Transition Metal Compound [RuCl₂(p-cymene)]₂ Ligand TT-CB4 Hydrogenation Substrate 2-Fluoroacetophenone

The results are shown in Table 12.

TABLE 12 Ruthenium/TT-CB4/2-Fluooacetophenone Reaction Time (hours) Conversion (%) Enantiomeric excess (%) 2 7 73.3 19 41 75.1 26 48 75.1 43 64 75.0 48.5 69 75.3 114.5 91 75.2

Comparing the results of Examples TH12 to TH14, it can be seen that the rates of these reactions are generally quite low. However, the presence of an electron-withdrawing group 2-fluoroacetophenone increases the rate of reaction. The enantioselectivities are high except in the case of the reduction of 2-fluoroacetophenone. This result is not surprising given that the fluoro substituent is in the ortho position. It can also be seen that the enantiomeric excess does not decrease over time as would be expected.

Example TH15

This Example describes the iridium catalysed hydrogenation of acetophenone using TT-CB4 as catalyst ligand. The hydrogenation procedure used was the same as that of Example TH10 (15% water)

The following reactants were employed.

Transition Metal Compound ¹[Ir(Cp)Cl₂]₂ Ligand TT-CB4 Hydrogenation Substrate (a)–(k) See below ¹ [Ir(pentamethylcyclopentadienyl)₂Cl₂]₂

a: R═H b: R═F h: R═CF₃

c: R═Cl d: R═Br i: R═OMe

e: R═F f: R═Br g: R═Cl

j

k

The results are shown in Table 13.

TABLE 13 Iridium/TT-CB4/ketones (a)–(k) Ketone Reaction Time (h) Conversion (%) Ee (%) a 140 90 82 b 51 83 85 c 91 89 76 d 91 93 76 e 68 86 36 F 163 65 29 G 163 89 24 H 43 95 86 I 150 22 78 J 139 41 91 K 139 77 73

Example TH16

Example TH15 was repeated but using CB-3.019 as ligand in place of TT-CB4.

The following reactants were employed.

Transition Metal Compound [Ir(Cp*)Cl₂]₂ Ligand CB-3.019 Hydrogenation Substrate Ketones (a)–(k)

The results are shown in Table 14

TABLE 14 Iridium/CB-3.019/ketones (a)–(k). Ketone Reaction Time (h) Conversion (5) ee(%) a 26 88 96 b 26 99 94 c 25 98 94 d 20 99 95 e 21 99 73 f 92 95 66 g 46 96 63 h 4 98 93 i 141 80 95 j 45 55 97 k 45 96 96

There are noticeable differences in the results obtained for ruthenium and iridium with ligand 1 (TT-CB4). Generally, the ruthenium system gives rise to higher enantiomeric excess and lower reaction rate, whereas the iridium system gives a higher reaction rate and a lower enantiomeric excess. However, the combination of iridium and ligand 2 proved to be most successful. The reactions tended to proceed rapidly with high enantioselectivity. For all systems, electron deficient ketones were reduced more quickly. This is best illustrated by comparing the results of the reduction of 3-trifluoromethylacetophenone and 4-methoxyacetophenone. Also, as expected, substrates with ortho-groups gave rise to a lower reactivity and enantiomeric excess.

Example TH17

In order to determine the effect of an increase in water concentration, the procedures of Examples TH14 and 15 were repeated but using a 2-propanol-water mixture containing (i) 34% and (ii) 51% water. The overall volume of reaction solvent remained unchanged.

The following reactants were employed.

Transition Metal Compound [Ir(Cp*)Cl₂]₂ Ligand (1) TT-CB4 Ligand (2) CB-3.019 Hydrogenation Substrate Ketones (a)–(k)

The results are shown in Table 15.

TABLE 15 Iridium/TT-CB4(1) or CB3.019(2)/Ketones (a)–(k) Reaction Conversion Ketone Ligand Time(h) (%) ee(%) b^(i) 1 22 74 92 b^(ii) 1 22 90 92 b^(i) 2 2.5 82 94 b^(ii) 2 2.5 94 93 e^(ii) 2 5 97 74 i^(i) 1 115 20 84 i^(ii) 1 115 33 91 i^(i) 2 116 76 92 i^(ii) 2 116 89 87 k^(i) 1 42 47 91 k^(ii) 1 42 66 93 k^(i) 2 18 92 95 k^(ii) 2 18 92 94 Table 3. Iridium systems containing (i) 34% and (ii) 51% water.

The results shown in Table 15 are surprising in that in expected rate decrease relating to the lower concentration of 2-propanol was not observed. Instead, a significant rate increase was noted for both the (i) 34% and (ii) 51% water systems. In addition to this, iridium-ligand 1 systems showed a large increase in enantiomeric excess when the concentration of water was increased form 15% to 34% (see F results shown in Table 13.).

Example LS18

This Example demonstrates the synthesis of a further ligand:

Example TH19

Bis-3,5-trifluoromethylacetophenone (1.32 g, 5.16 mmoles), dichloro(pentamethylcyclopentadienyl)rhodium(III) dimmer (7.4 mg, 11.97 micromoles), sodium (1S,2S) 4-(2-Amino-1,2-diphenyl-ethylsulfamoyl)-benzenesulfonate (11.2 mg, 25.92 micromoles), and 2.5 ml tetrahydrofuran were charged to a 25 ml flask and flushed with nitrogen. Water (12 microlitres, 0.66 mmoles) was added by syringe and the mixture was stirred for 20 minutes. A 2:5 molar ratio mixture of triethylamine and formic acid were added to the reaction at a rate of 1.5 ml/h for 2 h. At this time all the ketone had been converted to alcohol and the optical purity was determined to be 81% ee. The reaction was concentrated by vacuum distillation a sample A was taken for Rhodium analysis. To the concentrate, 3 ml toluene and 5 ml water was added, the aqueous phase separated and the organic layer divided into three portions B, C, D of 1 ml. To each portion was added 1.6 ml water. Sample B was concentrated to dryness. To sample C 100 mg of Amberlite™ IRA-93 was added and the mixture stirred for 2 hours, filtered and the filtrate concentrated to dryness. To sample D 100 mg of Dowex™ 1×8−50 was added and the mixture stirred for 2 hours, filtered and the filtrate concentrated to dryness. In sample B the concentrated filtrate was dark purple, whilst in samples C and D it was a light pink.

The samples were analysed by ICPMS for Rhodium and the following results were obtained:

Sample A 4930 ppm Sample B 1040 ppm Sample C  365 ppm Sample D  280 ppm

The results from the analysis of Samples C and D compared to Sample B show that treatment of the reaction mixture with ion exchange resins is effective in the separation of the catalyst from the reaction mixture. 

1. A catalyst having the general formula:

in which: R¹⁸ represents an optionally substituted hydrocarbyl or perhalogenated hydrocarbyl ligand; A represents —NR¹⁹—, —NR²⁰—, —NHR¹⁹, —NR¹⁹R²⁰ or —NR²⁰R²¹ where R¹⁹ is H, C(O)R²¹, SO₂R²¹, C(O)NR²¹R²⁵, C(S)NR²¹R²⁵, C(═NR²⁵)SR²⁸ or C(═NR²⁵)OR²⁶, R²⁰ and R²¹ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁵ and R²⁶ are each independently hydrogen or a group as defined for R²¹; B represents —O—, —OH, OR²², —S—, —SH, SR²², —NR²²—, —NR²³—, —NHR²³, —NR²²R²³, —NR²²R²⁴, —PR²²— or PR²²R²⁴ where R²³ is H, C(O)R²⁴, SO₂R²⁴, C(O)NR²⁴R²⁷, C(S)NR²⁴R²⁷, C(═NR²⁷)SR²⁸ or C(═NR²⁷)OR²⁸, R²² and R²⁴ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁷ and R²⁸ are each independently hydrogen or a group as defined for R²⁴; E represents a linking group comprising 2–4 carbon atoms linking A and B, said carbon atoms optionally carrying one or more substituents; M represents a Group VIII transition metal capable of catalysing transfer hydrogenation; and Y represents an anionic group, a basic ligand or a vacant site; provided that when Y is not a vacant site that at least one of A or B carries a hydrogen atom, characterised in that at least one of said groups R²⁰ to R²² or R²⁴ to R²⁸ is present in the form of an optionally substituted sulphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group, or an optionally substituted sulphonated heterocyclyl group.
 2. A catalyst according to claim 1 wherein A represents —NR¹⁹—, —NR²⁰—, —NHR¹⁹, —NR¹⁹R²⁰ or —NR²⁰R²¹ where R¹⁹ is H, C(O)R²¹, SO₂R²¹, C(O)NR²¹R²⁵, C(S)NR²¹R²⁵, C(═NR²⁵)SR²⁶ or C(═NR²⁵)OR²⁶, R²⁰ and R²¹ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁵ and R²⁶ are each independently hydrogen or a group as defined for R²¹; B represents —O—, —OH, OR²², —NR²²—, —NR²³—, —NHR²³, —NR²²R²³, or —NR²²R²⁴ where R²³ is H, C(O)R²⁴, SO₂R²⁴, C(O)NR²⁴R²⁷, C(S)NR²⁴R²⁷, C(═NR²⁷)SR²⁸ or C(═NR²⁷)OR²⁸, R²² and R²⁴ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁷ and R²⁸ are each independently hydrogen or a group as defined for R²⁴; and wherein at least one of R²⁰ to R²² or R²⁴ to R²⁸ is present in the form of an optionally substituted sulphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group or an optionally substituted sulphonated heterocyclyl group.
 3. A catalyst according to claim 2 wherein A is a group of the formula —NHR¹⁹ or —NR¹⁹— where R¹⁹ is represented by the group —SO₂R²¹ in which R²¹ is an optionally substituted sulphonated hydrocarbyl group, sulphonated perhalogenated hydrocarbyl group or optionally substituted sulphonated heterocyclyl group.
 4. A catalyst according to claim 3 wherein R²¹ is a sulphonated phenyl group having n sulphonate groups where n is 1 to
 5. 5. A catalyst according to claim 3 or 4 wherein B is —NH₂ or —NH—.
 6. A catalyst according to claim 1 wherein E is of the formula —CHR³⁰—CHR³¹— where R³⁰ and R³¹ are independently hydrogen or an optionally substituted hydrocarbyl group.
 7. A catalyst according to claim 1 wherein E has two carbon atoms linking A and B and is a bond in an optionally substituted cycloaliphatic ring.
 8. A catalyst according to claim 1 or 4 wherein R¹⁸ is an optionally substituted aryl or an optionally substituted alkene.
 9. A catalyst according to claim 8 wherein R¹⁸ is cymene.
 10. A catalyst according to claim 8 wherein R¹⁸ is a pentamethylcyclopentadienyl group.
 11. A catalyst according to claim 1, wherein M is ruthenium, rhodium or iridium.
 12. A catalyst according to claim 1 or 4, in which A—E—B comprises at least one stereospecific centre.
 13. A process for the preparation of a catalyst according to claim 1 or 4 which comprises reacting a metal aryl halide complex or a metal alkenyl halide complex with a compound of formula A—E—B or a protonated equivalent from which it may be derived.
 14. A ligand having the following formula:

in which: W represents —OH or —NH₂; R³² represents an aryl group having at least one —SO₃H or —S₃M¹ substituent wherein M¹ is an alkali metal and is further optionally substituted; and R³³, R³⁴ are independentiy optionally substituted hydrocarbyl groups or R³³ and R³⁴ are optionally linked in such a way as to define an optionally substituted ring.
 15. A ligand according to claim 14 in which R³² is a phenyl group having one —SO₃H or —S₃M¹ substituent.
 16. A ligand according to claim 14 or 15 in which R³³ and are independently phenyl.
 17. A ligand according to claim 14 or 15 in which R³³ and R³⁴ are linked so as to define a cyclohexyl ring.
 18. The compound:

and salts thereof.
 19. The compound:

and salts thereof.
 20. The compound:

and salts thereof.
 21. The compound:

and salts thoroof.
 22. A process comprising reacting a di-sulphide of formula:

with an oxidant to produce a compound of formula:

wherein: W is —OH or —N H²; R³² is an aryl group having at least one —SO₃H or SO₃M¹ (M¹ =alkali metal) substituent; R³⁵ is an aryl group; and R³³, R³⁴ are independently optionally substituted hydrocarbyl groups or R³³ and R³⁴ are optionally linked in such a way as to define an optionally substituted ring.
 23. A process according to claim 22 wherein the substitution pattern of the aryl group R³² is such that the —SO₃H or SO₃M¹ (M¹=alkali metal) substituent is positioned para with respect to the SO₂NH—CHR³⁴—CHR³³—W group.
 24. A process according to claim 22 or 23 wherein the oxidant is alkaline hydrogen peroxide.
 25. A process for the transfer hydrogenation of an organic compound having a carbon-carbon or carbon-heteroatom double bond, said process comprising reacting the organic compound with a hydrogen donor in the presence of a catalyst having the general formula:

in which: R¹⁸ represents an optionally substituted hydrocarbyl or perhalogenated hydrocarbyl ligand; A represents —NR¹⁹—, —NR²⁰, —NHR¹⁹, —NR¹⁹R²⁰ or —NR²⁰R²¹ where R¹⁹ is H, C(O)R²¹, SO₂R²¹, C(O)NR²¹R²⁵, C(S)NR²¹R²⁵, C(═NR²⁵)SR²⁶ or C(═NR²⁵)OR²⁶, R²⁰ and R²¹ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁵ and R²⁶ are each independently hydrogen or a group as defined for R²¹; B represents —O—, —OH, OR²², —S—, —SH, SR²², —NR²²—, —NR²³—, —NHR²³, —NR²²R²³, —NR²²R²⁴, —PR²²— or —PR²²R²⁴ where R²³ is H, C(O)R²⁴, SO₂R²⁴, C(O)NR²⁴R²⁷, C(S)NR²⁴R²⁷, C(═NR²⁷)SR²⁸ or C(═NR²⁷)OR²⁸, R²² and R²⁴ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁷ and R²⁸ are each independently hydrogen or a group as defined for R²⁴; E represents a linking group; M represents a metal capable of catalysing transfer hydrogenation; and Y represents an anionic group, a basic ligand or a vacant site; provided that when Y is not a vacant site that at least one of A or B carries a hydrogen atom, characterised in that at least one of said groups R²⁰ to R²² or R²⁴ to R²⁸ is present in the form of an optionally substituted suiphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group, or an optionally substituted sulphonated heterocyclyl group.
 26. A process according to claim 25 wherein A represents —NR¹⁹—, —NR²⁰—, —NHR¹⁹, —NR¹⁹R²⁰ or —NR²⁰R²¹ where R¹⁹ is H, C(O)R²¹, SO₂R²¹, C(O)NR²¹R²⁵, C(S)NR²¹R²⁵, C(═NR²⁵)SR²⁶ or C(═NR²⁵)OR²⁶, R²⁰ and R²¹ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁵ and R²⁶ are each independently hydrogen or a group as defined for R²¹; B represents —O—, —OH, OR²², —NR²²—, —NR²³—, —NHR²³, —NR²²R²³, or —NR²²R²⁴ where R²³ is H, C(O)R²⁴, SO₂R²⁴, C(O)NR²⁴R²⁷, C(S)NR²⁴R²⁷, C(═NR²⁷)SR²⁸ or C(═NR²⁷)OR²⁸, R²² and R²⁴ each independently represents an optionally substituted hydrocarbyl, perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, and R²⁷ and R²⁸ are each independently hydrogen or a group as defined for R²⁴; and wherein at least one of R²⁰ to R²² or R²⁴ to R²⁸ in the form of an optionally substituted sulphonated hydrocarbyl group, a sulphonated perhalogenated hydrocarbyl group or an optionally substituted sulphonated heterocyclyl group.
 27. A process according to claim 26 wherein A is a group of the formula —NHR¹⁹ or —NR¹⁹— where R¹⁹ is represented by the group —SO₂R²¹ in which R²¹ is an optionally substituted sulphonated hydrocarbyl group, sulphonated perhalogenated hydrocarbyl group or optionally substituted sulphonated heterocyclyl group.
 28. A process according to claim 27 wherein R²¹ is a sulphonated phenyl group having n sulphonate groups where n is 1 to
 5. 29. A process according to claim 27 or 28 wherein B is —NH₂ or —NH—.
 30. A process according to claim 25 or 28 wherein E has 2, 3 or 4 carbon atoms linking A and B, said carbon atoms optionally carrying one or more substituents.
 31. A process according to claim 30 wherein E is of the formula —CHR³⁰—CHR³¹—where R³⁰ and R³¹ are independently hydrogen or an optionally substituted hydrocarbyl group.
 32. A process according to claim 30 wherein E has two carbon atoms linking A and B and is a bond in an optionally substituted cycloaliphatic ring.
 33. A process according to claim 25 or 28 wherein R¹⁸ is an optionally substituted aryl or an optionally substituted alkene.
 34. A process according to claim 33 wherein R¹⁸ is cymene.
 35. A process according to claim 33 wherein R¹⁸ is a pentamethylcyclopentadienyl group.
 36. A process according to claim 25 or 28 wherein M is a group VIII transition metal.
 37. A process according to claim 36 wherein M is ruthenium, rhodium or iridium.
 38. A process according to claim 25 or 28 wherein the organic compound to be hydrogenated is a ketone, an amine or an iminium salt.
 39. A process as claimed in claim 25 or 28 wherein the organic compound to be hydrogenated is of formula (I):

wherein: X represents O, S, CR³R⁴, NR⁵, (NR⁶R⁷)⁺Q³¹, N⁺R⁸—O⁻, (NR⁹OR¹⁰)⁺Q⁻, NNR¹²R¹³, NNR¹²SO₂R¹⁶, NNR¹² COR¹⁷, (NR¹¹NR¹²R¹³)⁺Q³¹, (NR¹¹NR¹²C(═NR¹⁴)R¹⁵)⁺Q⁻, (NR¹¹NR¹²SO₂R¹⁶)⁺Q⁻, (NR¹¹NR¹²COR¹⁷)⁺Q⁻, NP(O)R¹⁵R¹⁶, NS(O)R¹⁵ or NSO₂R¹⁵, Q⁻ represents a monovalent anion; R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹ R¹², R¹³ and R¹⁴ each independently represents a hydrogen atom, an optionally substituted hydrocarbyl, a perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group, one or more of R¹ and R², R¹ and R³, R¹ and R⁵, R¹ and R⁶, R¹ and R⁸, R¹ and R⁹, R¹ and R¹¹, R¹ and R¹¹, R¹ and R¹², R² and R⁴, R² and R⁷, R² and R¹⁰, R³ and R⁴, R⁶ and R⁷, R⁹ and R¹⁰, R¹¹ and R¹², and R¹² and R¹³ optionally being linked in such a way as to form an optionally substituted ring(s); and R¹⁵, R¹⁶ and R¹⁷ each independently represents an optionally substituted hydrocarbyl, a perhalogenated hydrocarbyl or an optionally substituted heterocyclyl group.
 40. A process as claimed in claim 25 or 28 wherein the organic compound to be hydrogenated is prochiral and the catalyst is chiral, an enatiomerically and/or diastereomerically purified form of the catalyst being employed, whereby the organic compound is asymmetrically hydrogenated.
 41. A process according to claim 40 in which A—E—B comprises at least one stereo specific centre.
 42. A process according to claim 25 or 28 in which the hydrogen donor is selected from hydrogen, primary and secondary alcohols, primary and secondary amines, carboxylic acids and their esters and amine salts, readily dehydrogenatable hydrocarbons, clean reducing agents, and any combination thereof.
 43. A process according to claim 42 wherein the hydrogen donor is isopropanol.
 44. A process according to claim 25 or 28 wherein the process is carried out in the presence of a base having pK_(a) of at least 8.0.
 45. A process as claimed in claim 25 or 28 wherein the catalyst is used in the form a supported liquid phase catalyst.
 46. A process as claimed in claim 25 or 28 which comprises an additional step of adding an ion exchange resin after reacting the organic compound with the hydrogen donor in the presence of the catalyst.
 47. A process according to claim 22 wherein R³³ and R³⁴ are independently phenyl or R³³ and R³⁴ are linked so as to define a cyclohexyl ring.
 48. A process according to claim 24 wherein the oxidant is a mixture of sodium hydroxide solution and hydrogen peroxide solution. 